/*
Adapted from: http://free-electrons.com/pub/mirror/devmem2.c

Forked because of the unpredictable access widths:
https://bugs.busybox.net/show_bug.cgi?id=10171
*/

#include <ctype.h>
#include <errno.h>
#include <fcntl.h>
#include <signal.h>
#include <stdint.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <sys/mman.h>
#include <sys/types.h>
#include <termios.h>
#include <unistd.h>

#define FATAL do { fprintf(stderr, "Error at line %d, file %s (%d) [%s]\n", \
  __LINE__, __FILE__, errno, strerror(errno)); exit(1); } while(0)

int main(int argc, char **argv) {
	int access_type = 'w';
	unsigned long map_size, map_mask;
	off_t target;
	uintmax_t read_result, writeval;
    int fd;
    void *map_base, *virt_addr;

    map_size = sysconf(_SC_PAGE_SIZE);
    map_mask = map_size - 1;
	if(argc < 2) {
		fprintf(stderr, "\nUsage:\t%s { address } [ type [ data ] ]\n"
			"\taddress : memory address to act upon\n"
			"\ttype    : access operation type : [b]yte, [h]alfword, [w]ord\n"
			"\tdata    : data to be written\n\n",
			argv[0]);
		exit(1);
	}
	target = strtoul(argv[1], 0, 0);

	if(argc > 2)
		access_type = tolower(argv[2][0]);


    if((fd = open("/dev/mem", O_RDWR | O_SYNC)) == -1) FATAL;
    printf("/dev/mem opened.\n");
    fflush(stdout);

    /* Map one page */
    map_base = mmap(0, map_size, PROT_READ | PROT_WRITE, MAP_SHARED, fd, target & ~map_mask);
    if(map_base == (void *) -1) FATAL;
    printf("Memory mapped at address %p.\n", map_base);
    fflush(stdout);

    virt_addr = map_base + (target & map_mask);
    switch(access_type) {
		case 'b':
			read_result = *((uint8_t *) virt_addr);
			break;
		case 'h':
			read_result = *((uint16_t *) virt_addr);
			break;
		case 'w':
			read_result = *((uint32_t *) virt_addr);
			break;
		case 'q':
			read_result = *((uint64_t *) virt_addr);
			break;
		default:
			fprintf(stderr, "Illegal data type '%c'.\n", access_type);
			exit(2);
	}
    printf("Value at address 0x%jX (%p): 0x%jX\n", (uintmax_t)target, virt_addr, (uintmax_t)read_result);
    fflush(stdout);

	if(argc > 3) {
		writeval = strtoul(argv[3], 0, 0);
		switch(access_type) {
			case 'b':
				*((uint8_t *) virt_addr) = writeval;
				read_result = *((uint8_t *) virt_addr);
				break;
			case 'h':
				*((uint16_t *) virt_addr) = writeval;
				read_result = *((uint16_t *) virt_addr);
				break;
			case 'w':
				*((uint32_t *) virt_addr) = writeval;
				read_result = *((uint32_t *) virt_addr);
				break;
			case 'q':
				*((uint64_t *) virt_addr) = writeval;
				read_result = *((uint64_t *) virt_addr);
				break;
		}
		printf("Written 0x%jX; readback 0x%jX\n", (uintmax_t)writeval, (uintmax_t)read_result);
		fflush(stdout);
	}

	if(munmap(map_base, map_size) == -1) FATAL;
    close(fd);
    return 0;
}